Automatic transfer panel



June 1, 1948. J. H, WALLACE Er AL I AUTOMATIC TRANSFER PANEL Filed Oct.16, 1945 QSANWN x www www Patented June 1, 1948 UNITED sTATefgs PATENTformer:

. Los Angeles, 'Calif.,vassgnors,'by :mesme-assign- :.ments, toEngineering Controls, Inc.,acorpo rationof-California 4-Glaims. Y V1"Thislinfvention relatesto an apparatus for automatically transferringelectrical loads from -one electrical. generatorfto lanother.

*j-In many situations there are `two electrical =loads, each of which isnormally supplied with Acu-rrentirom its ownrelectric generator whereinthel'load -is -such Ethat serious results 'follow Yif -an electricgenerator supplying one of the loads -fails evenifor a--very shortperiod of time. It-has-been proposed to-employ two generators which'nor- -vnmallyfcarry the twoloadsandtoprovide athird or standbygenerator which can `be employed to `carry theload ofvwhichever'generator -may fail.

An'object of thepresent invention is Kto provide `an apparatuswhichin-"the event of-failure ofone i ofgthe two generatorscarrying theirrespective loadsfwill-promptiy and automatically cause'thethirdor'standbygeneratorto'loe-started up andto carry the load Aofvwhichevergenerator*may have failed.

In `some instances, .serious results ensue when 'anelectrical load-'hasits Ycurrent supply-cut o even foraiveryshortfraction oftime sothat itis impossible' to` wait until *the third orLstandloy'generatoriis-brought'up to speed andls in a conditionto have'the load Yof `the generator .that failed transferredthereto. VAItis,'therefore, another ob- `ject :ofztheV invention -to ,provide vswitchgear for zthejpurposenf transferring two loads among 4threergeneratorsin such a manner that ineither Aload visdmpped'for alongerperiod o'f time .than that ireguiredorithe opening of one magneticcontactor Vand-the closing of another, andis so arranged'thatenltheevent of'failure of either/generatoriits "loa'd'is `instantlytransferred to .the other running generator which is caused to carryboth Aloadstemporarily while the standby Agen- .eratorisautomatlcallystartedand when the latteris developing normal potentialthe load 'from Ythefalll-:fcl generatoris transferredthereto. Un-`dersuch circumstances, the generator whichhas continued running istemporarily overloaded beingreguired to carry .both loads which mayexceed vthe capacity vfor which'the .generator was devSigned. L'However,thetimerequired to bring 'up "thes'tandbygenerator to vspeed ls.usuallysufliclentlyshort sothat the` overloading of therunningigenerator is not disastrous. In .accordance 'withthev presentinventionthe ratings of the'three generators used will be Aselectedsufficiently -high so that-the temporary overload can -be carriedl'nyanyrgeneratorwithout involving excessive volt- Llrgefrlrop-Stlllanother object of-the `Vinvention is to prov-idefanapparatus--whereln there'are two loads and three. generators, two f of thegenerators serving to normally carry :the .respective Lloads, and thethird vgenerator serving as a 4standby .generator and which is highly`versatile in that .any twoof .the three generators maybe causedftocarry ieitheref the atwo .loads with the remaining gencrater .serving asa Vstandhyi'generator ,for -either of the other :two .or .workinggenerators.

With the foregoing andetherobjects inwiew, :which willlbezmade manifest:in the.followingide- .tailed -description andA specifically .pointed.out in the ,'appended.- claims, yreference yis :had to the accompanying:drawings ;ior Aan Yillustrative rembodimen-t of .the invention,V,tv-herein ,the-iigure is apartial schematic A'wiring diagram of .theapparatus embodying :the .present invention, some; of the connectionsbeing omitted for purposes ;of clarity fand represented r-merely `bycorresponding letters -at the ends of `.the omittedy connections.

Referring-.tothe accompanyingrdrawing,mand Ll indicate the leads of twoloads represented on :thedrawingfasload, A..andloadB. zfl'2, I:3,.and 14indicate :leads :from Ythree generators, -fnamely generators 'TGI G2,4and G3, l.two of which lnormally designated carry floads A and fB,`respetar-- tively, andthe third of which serves-as .a :stand- VVbygenerator vwhich ymay A-be caused to .assume either -loa'd -A or -load BYintheevent that-one of 'the .'runninggenerators -should fail. Between4the generators and the loads there-are two'banks of load-switchingcontactors indicated at lA, v'ZAAUL rvand lBZB, and 3B. fEach.contactor'hasa coilfor solenoid which-aetuates its contacts, Ythere'being two normally open pairs o'f contacts andtwo-nor'- mally closedr-pair -of contacts associated with Leach coil. -Eachload-swltching lcontacter serves to electrically connectitsload -withits respec- -tivegenerator, thus load-switching contacter IA -ser-ves lto Yconnect loadJA-with 'generator Gl and disconnect it -therefrom. Load-switchingcontactor 2A serves -to lconnect generator G2 with 'load JA anddisconnect -it `therefrom 4and loadswitehing Vcontacter -3-A Cserves 'to-ccnnect gen- 1eratorG3 with load "Ayanddisconnect ittherefrom. `Inasimilar-manner; load-switching-contactor iB, *2B, and `3Bserveftoconnect generators -`G|, Gland G 3wi thloadjB'and-disconnect themVtherefrom respectively.

As vpart-ofthe apparatus there are two load selectors indicated -as 1load vA selector and load-B selector. Each 'selector has -three.component switches `indicated -by =numerals ASl, YKS2, and A53; BSL*BSL -and fBS-3, respectively. These switches are so arrangedmechanically that 'only one :switch mayebe closed -in-'each loadselector,

the other two being required to be kept open. These load selectors areused to optionally control the load-switching contactors so that any hasa coil operable when energized to simultaneously open all of thenormally closed contacts associated therewith. The various parts andterminals I are electrically connected together as period whengenerators GI and G2 were carrying loads A and B, respectively, coils 41and 48 were energized holding the contacts associated therewith in openposition. Generator G3 being inillustrated upon the drawing, the variousconnections being referred to hereinafter in the course` of thedescription of the operation of the apparatus which is substantially'asfollows:

In a typical situation generator GI is supplying electric current toload A. Generator G2 is simulof the. three generators. Inthe usualsituation taneously supplying current to load B. Generator n G3 is notrunning and serves as a standby generator for either of generators GIand G2. When generator GI isV operating and iselectricallyconnectedtoload A, component switch-ASI ofload A selector is closed, andcomponent switches AS2 and ASB of. load A selector are held open: W'hengeneratorv G2 is connected to load B, component lswitch BS2 of load Bselector is closed and component sWitchesBSI and BSS of load B selectorare open. Under these circumstances, a circuit is closed from one sideof generator GI through line.I5, I6, closed contacts I1, line IS'to coilI9 of 'load-switching contactor IA. The .balance of the circuit lleadingthrough normally closed contactsZ of load-switching contactor 2A andnormally closed contacts 2l of load-switching contactor 3A, and thenceto the other lead from generator GI.V When coil I9` is-energized twonormally open contacts 22 and23 are closed thus connecting the leads I2of generator GI directly to load A. In a similar manner generator G2supplies, current from one side to lines 24 and 25 to closed contacts.26of component switch BSZ of load B selector and thence through line 21 tocoil 23 of load-switching'contactor 2B. The balance of thecircuit` isthrough normally closed contacts 294 of the load-switching contactor IBand' normally closed contacts 30 ofjload-switchingcontactor 3B to theother side of generator 2. ,Coilzav being thus energized closesitsnormally Open contacts 3IA and 32, V thus connecting generatorGZYdirectlyto load B,.j

Assume for` purposes o f illustration that under these circumstancesgenerator GI should fail.

Upon a failure of current to reach coil I9 of loadswitching contactor IAfromgenerator GI this coil becomes deenergized permitting its contacts2,2 and23 to open'andits normally closed contacts ,'33 and 34to close.Current may then flow from Vgenerator G2v through normally closedcontacts 35 of load-switching contactor 3Athrough closed contacts 34 toone terminal of c oil36. `".Ihe current path to the other side of coil36 will hereinafter be explained in connection with the de- V scriptionof `thev deenergizing of this coil. When coil V36 is thusenergized from generator G2 it closes its normal1y'open-,contacts 31 and38 and"` opensnormallyclosed contacts 26 and 39. Contacts 31 and 38on-being closed thus'connect load A directly with generatorvGZ it beingunderstood `that generator G2 is already supplying current to load'Bthrough contacts 3| and 32.

y The three generators are each also connected by lines 4I, 42, 43, 44,45, and 46Vto coils 41, 48, and 49 of the circuit control relays.`r'lhesecircuit control relays each have a igroup of normallyVclosedcontacts associated therewith During the Voperative and thereforesupplying noV current to coil 49 this coil would be deenerg'ized and itscontacts would be closed. Uponthe failurefof generator GI contactsassociated with coil 41 are permitted to close as soon as coil 41becomes deenergized so that upon the failure of generator GI allcontacts of the circuit control relays are 'closed with the exception ofthose associated with lcoil '48, which is in turn associated withgenerator G2'Which is still operating. Among other functions the"circuit control relays control three starting control circuits whichstart up the operation of relay coil l41, causing-rthe-contactsassociated therewith to return to their normally closed position. Thestarting control circuit governing the starting of generator 3 is thusclosed, such circuit being traceable throughline 56, through the manualautomatic switch Vgenerally indicated at 5I, line 5-2, contacts 53, andline .54.V In each of the starting control circuits there isanindependent source of power such asthe three 55. With the startingcontrol circuit for generator G3 thus Y closed and energized by 4itsbattery 55, generator G3 is started in operation `and'is brought up tonormal operating conditions as soon as is reasonably possible so thatthe overloading or doubleloading of generator G2 -will beV minimized toas short aperiod of time as possible. When generator'G3 isbrought'up tospeed'it of course energizes relay coil 4.9, being-connected thereto bylines 45 and 46.' The bank of relay contacts associated with thisrelayjcoil are consequently opened. Op'eningof contacts 56 breaks thecircuit thro'ughload-switching contactorcoil 36, the circuitbeingtrace'able as `follows: From line 44I through contacts 51, line 53YtoV contacts? 56,

4through line159, the'manual automatic switch 5I,

were consequently requiredtojbe kept open. However, Vas loadA' selectorAS Il has remained closed Vregardless 'of` the failure ofjgenerator Gigcurrent V iiow could takjplac across contacts 63t'o` line 64 to line 66t load-switchingcontactoi. coil 36,

.and from this coil the circuit is completedthrough contacts 34 andcontacts'35-to the' other lead from generator G2.; VYWhen Ygenerator VG3vhasbeen brought up to,speedload-switchingV contactor' Acoil 61 isenergized, the circuit beingtraceable-'from onefside' of generator G3through line VIl'thro'ugh closed contacts `33an`d vclosed cntacts39which contacts Ywill have returned toftheir normally closed position dueto the deenergizingiof coil 36.

.From `contacts 39 the circuit continues-through coil 61, line 69,Y andline 13 to contacts 1410il load A Selector. ASI which isistill closd-:Thse coili'acts being 61056261111v linel; sag-,sentiers thefcrr cui-ttothe other contact 12 of load A selector AS2 land thence -via line "IBthrough the manualautomatic switch "to -contact The contacts of thecircuit control 'relays S landT will of cou-rse beV open-due to thecontinued energizing .of coil 48 by generator G2. However, contact T -of`circuit control relay 2 is .directly connected to the cor-responding`contact T of load B selector lB82 andas -this selector 'has remainedclosed, the circuit .is completed vbetween T and S .of loadB selectorBSZ, the fS terminal Vbeing .directly `connected to the .S terminal orcontact of circuit control relay R2. From this-contact line 17| leadsthrough closed contact .11a which have been closed .due to .the.deenergizing Aof coil :41 to line 46, .thus .completing .the circuit.The .energizing of load-'switching contacter coil 4|i'| which takesplace .substantially simultaneously with the .deenergizingcf coil z36vand .open contacts 21 and A3.1i and close contacts 18 and 129, .thus.automatically placing generator G3 .on the line Aand causing .it toassume and carry load A.

In `this .manner if generators Gil. and G2 are initially carrying loadsA and B, respectively, and generator Gl should fail, load A is:instantly and automatically :connected .to generator IG2 so thatgenerator G2 is Vfor a short period of time carrying :both load A andload B while generator `G3 is being brought up to full operatingconditions.

When generator G3 has been 'brought -up to normail load A isautomatically disconnected from generator G2 and connected to .generatorG3 which will .continue to carry this 'load until such time as othermodifying conditions occur.

If generatorGl is repaired during the time that load .A is being carried'by generator G3 and it is desired `to 'have .generator G| lresume loadA in place .of generator G3 `the mere 'bringing up :of generator Gl tooperating .conditions will cause circuit control relay coil -41 :to'beenergized VKwhich will open `contacts 18 which breaks the circuitthrough vcoil '57| thus opening contacts v|8 .and :19 .and takinggenerator G3 off load .A. Simultaneously, on the @deenergizing of Vcoil:6.1 contacts 2| and willlagain close and on .the .closingofcontacts 2|a circuit is completed vthrough :coil yI9 permitting 'this coil to becapable of being energized by generator Gl and to connect load A withgenerator GI on the closing oi contacts 22 and 23.

In the foregoing description generators G| :and G2 were assumed to becarrying loads A and B respectively, and generator Gl was assumed tofail. If generators GI and G2 are carrying loads A and B, respectively,and generator G2 should fail va similar sequence of operations wouldtake place. Thus, on the failure of vgenerator .G2 load- /switchingcontactor coil 28 would be deenergized allowing its contactors 3| and 32to open and its contacts 80 and 8| to close. On closing of contacts 80current may flow from generator GI through contacts 83, line 84, closedcontacts 80 to coil 85, thence through line 8B and line |04 throughcontacts 88 of load B selector BSZ, through lines 90, |05, andthe'manual-automatic switch 5| to contacts EF of circuit control relayR2. These contacts having been closed due to the failure of generator G2having deenergized coil 48, current may flow through contacts IJ whichremain closed as long as generator G3 is not operating. Contact J isdirectly connected t0 line 42 of generator G| thus completing thecircuit. When coil 85 is thus energized because of the failure ofgenerator G2, generator GI is caused to assume load B by the closing ofcontacts 9| and 92 so that this generator is temporarily VBIS carryingloadB infaddltion to V'load A which it was initially carrying.

When the failure of generator G2 .causes coil 48 to be deenergized.contacts 93 were permitted to `close which closes the .circuit for theengine starting controler generator G3, this .circuit .being traceablethrough line 50, manualfautomatic switch 5|,line 52, andcontacts 93.Generator .G3 is consequently Astarted up and when brought :to operatingcondition it Ywill .energize coil ,19. opening of the normally closedYcontacts .associated with .this .coil :breaks the circuit through coil'85, this `circuit .being traceable `from generator 4Gl through`contacts 33, contacts r8.0, .coil .85, line 6, .and line -iI-ill,across contacts $8 through lines .1| 0.5, 80, .and the manual-.automaticswitch 5|, thence .across contacts 94 to contacts 95,'.and1thence toline .42. Theopening of .contacts 05 breaking .the .cir-.cuit vthrough.coil .8,5 when generator G3 .comes .up to speed results in 'load Bbeing taken oif `generator yGl. Simultaneously therewith, on .opening ofcontacts i load `switching .contacter coil 196 may be .energizcdbyfaenerator G3, :the circuit being traceable from generator :G3 throughline V91, :contacts All, coil 9 6, lines 1.06 Vand :l 01, acrosscontacts .9.9 of ,load 5B selector BSZ through the manualfautomaticswitch 51| and contacts @|00 which Iwill athen Ahave .been closed due tothe -deenerlgizingof coil 48 .on vaccountof the failure .of l.generatorG2. The circuit .then continues to terminals :CD .of contacts associatedwith coil ,4.1 These termin-als -arc di- -rectly connected to contactsCD .of yload Aselector AS=| which still v-stands in closed position sothat, .although contacts -|0| :between 'terminals 1CD of cir-cuit relayRI areonpen, the circuit is completed through load A selector ASI toterminal `C incir- Acuit control relay lt| .to line 4.6. The .energizingof coil :9.6 closes contacts |02 ,and l.|03 ,and...opens contacts .83'and.30, .thus causing generator ,G3 to assume load B. If generator G2is then repaired and started up .in operation it will zautomatically.disconnect generator G3 from Aload B and'assume load B itself. Thus,when generator G2 is brought up to operating .conditions coil 448 will.on being energized open contacts |00 which are .incircuit with -coilv$1.6 as previously explained, and .when the circuit of coil 96 is thusbroken generator .G3 will be taken off of load B on the openingoflcontacts |02 and .|03. The closing .of ^contacts 30 closes Vthe.circuit through ,coil 23 so that j.this c Oil may again beenergized by.generator `G2 -to .cause generator G2 to again be .connected .with.load B .on .theclosingof contacts 3| .and .32. y

r[he foregoing .description has been .based on v.the assumption thatgenerator .Gl isnormally connected to load A and generator G2 normallyconnected to load B with generator G3 acting as a standby generator forgenerators GI and G2 susceptible of being optionally connected to eitherload A or load B depending on whether generator G| failed or generatorG2 failed. For such purpose only a portion of the apparatus illustratedwould be required, it being obvious that only load selectors ASI and BSZhaving been utilized in the description so far. By using two banks ofthree load selectors as illustrated, the arrangement is quite versatilein that any two of the three generators may be used to carry either ofthe two loads with the third generator functioning as a standbygenerator. Thus, in the load A selector bank if load A selector AS2 willbe connected to normally carry load A and if load A selector AS3 isclosed in lieu of AS2, generator G3 will be normally connected to carryload A. Likewise, in

to normal operating speed. The failurev of a loaded generator causes its4circuit control relay to close a circuit through the engine startingcontrol circuit of the standby generator to start up the standbygenerator and when the standby generator is brought up to speed'thecontacts thatV connect the loaded generator that has not failed andwhich is carrying the second load to open so that the generator that hasnot failed may thereafter continue to carry only its own load. Thestandby generator is automatically connected to the load of thegenerator that failed.

The specific manner in which the foregoing is accomplished on theassumption that other generators are normally carrying loads A and Bbesides generators Gl and G2 are not described herein for the sake ofbrevity. They may be traced, however, on various assumed conditions inamanner similar to that previously described in connection with thewiring diagram. It should be kept in mind, however, that all letteredcontacts or terminals on the circuit control relays VareV connecteddirectly to the correspondingly lettered points on the load selectorbanks which, when the load selectors are closed, provide or close shuntcircuits around contactsof the circuit control relays when thesecontacts would be open and when it is necessary to complete the circuitacross them.

In the above-described switch gear the presence of the auxiliarycontacts 33, 34, 20, 39, 2|, 35, 95, 29,780, 8|, 83, and 30 on the loadswitching contactors prevents the closing of more than one generator toeither load. Consequently'it is impossible to parallel two generatorstothe same load.

, Various changes may be made in the details of construction withoutdeparting from the spirit and scope of the invention as dened by theappended claims.

We claim:

1. In combination, two electrical loads and three generators, meansnormally connecting two of the three generators to their respectiveloads, means operable by the failure of one'of the loaded generators forcausing the other loaded generator to assume its load, and meansoperableby the third generator coming upto normal operating conditions for,disconnecting; the assumed load from the loaded generator and causingthethird generator to be connected tothe assumed load.

2. In combination, vtwo electrical loads and three generators, two ofwhich are normally connected to their respective loads, means operableby the failure of one of the loaded generatorsA for causing its load tobe assumed by the other loaded generator, means operable by the failureofthe mentioned generator'for starting up theV thirdV generator, andmeans operable upon the third generator coming up to speed fordisconnecting the assumed load from the loaded generator and connectingit to the third generator.

3. In combination, a pair of electrical loads, three generators, two ofwhich are adapted to be normally connected to the two loadsrespectively. load-switching contactors for connecting the generators tothe loads, load selectors for controlling the load-switching contactorsand cir. cuit control relays operatively connected Vto theload-switching contactors and load selectors in such a manner that uponfailure of one loaded generator its load will be temporarily assumed vbythe other loaded generatorand upon thevthird generator becoming capableof assuming a` load, the assumed load will be disconnected from'theloaded generator and automatically connected, to

Number the third generator.

4. In combination, a pair of electrical loads, three generators, two ofwhich are adaptedtoibe normally connected to the two loads respectively,load-switching contactors for connecting the generators to the loads,load selectors for controlling the load-switching .contactors andcircuit control relays operatively connected .to the load-switchingcontactors and load selectors in such a manner that upon failure of oneloaded generator its load will be temporarily assumed by the otherloadedgenerator and upon thethird generator becoming capable of assuming aload, the assumed loadrwill be disconnected'from the loaded generatorand automatically connected to the third generator, the load selectorsbeing characterized by closing shunt circuits across contacts of circuitcontrol relays.

' JOHN H. WALLACE.

ALVIN J SMITH.

i Y REFERENCES CITED UNITED STATES PATENTS Name Date 1,793,384VAndersonV Feb. 17, 1931

